Capping is a common remediation technology for the containment/stabilization of contaminated sediments. During capping activities, capping material is commonly released from a barge at the water surface and falls through the water column to the sediment surface, thus providing a clean surface sediment layer. Little information exists on the potential release of contaminated sediments during and after the capping operations. This report focuses on the measured release contaminants during individual capping events at two Confined Aquatic Disposal Cells (CADs) located in the Mystic River, Boston, MA. The two CADs (M8 and M19) were previously filled with dredged material contaminated with total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). U.S. EPA/ORD sampled the water column during each capping event to evaluate whether cap placement resulted in the release of contaminated sediments. Results showed capping from the water surface resulted in contaminant resuspension with the most significant releases occurring during the application of the first layers of capping material. With each subsequent layering of the capping material, levels of contaminant resuspension decrease with each successive application.